This invention relates to a technique for a charge neutralizer for neutralizing electric charge caused by ion irradiation during sample observation with a scanning ion microscope.
The basic configuration of a focused ion beam device is shown in FIG. 6. Reference numeral 1 denotes a liquid metal ion source, 3 is a ion optical system for producing a focused ion beam 2, and 4 is a deflector for deflection scanning of the focused ion beam 2. When the ion beam is irradiated on a sample 9 placed on a sample stage 7, secondary charged particles such as electrons or ions are caused to be ejected from the irradiated part. Reference numeral 5 denotes a secondary charged particle detector which captures and detects the secondary charged particles. The detection signal can be input to a computer 10, where correspondence to the beam scanning position is checked and shown on the display 11 as a scanning ion microscope image. The focused ion beam device not only has a function as a scanning ion microscope, but also a maskless etching function and a maskless deposition function realized by irradiating the focused ion beam, but gas assist etching is also realized by irradiating the ion beam by spraying assist gas, such as a halogen, from a gas gun 6, and deposition can be performed, in which a film is formed on the surface of the sample by irradiating the ion beam by spraying material gas from the gas gun 6.
When the beam of charged particles such as ions is irradiated on the sample surface, the charge of the charged particle is injected into the sample. The sample then radiates the secondary charged particles, and takes a differential charge. Generally, this phenomenon is called charge-up. Depending on the charge-up conditions on the sample surface, the amount of radiated secondary charged particles due to the beam irradiation changes. For example, suppose that the beam of charged particles is the focused ion beam carrying the positive charge, and the sample surface is charged-up with a positive charge by irradiating the ion beam on the sample surface. Then, the potential of the sample surface increases and has the effect of holding the negative secondary electrons carrying negative charge discharged from the sample surface. On the contrary, when the secondary ion carries positive charge, it has a repulsion effect and makes discharge easy. As a result, this charge-up phenomenon is deemed undesirable in the scanning microscope field, where secondary electrons or secondary ions are detected to derive the surface image, because the amount of the radiated secondary charged particles is affected by the physical conditions due to the charge-up of the surface, which has no relation to the material or shape of the sample surface. Also another problem arises in the case where the sample or the area near the area where electrons are irradiated is asymmetrical in terms of electrical resistance, in that the path of the irradiated beam is affected, and causes beam drift.
Reference numeral 8 of the focused ion beam device shown in FIG. 6 represents a charge neutralizer, which is capable of neutralizing electric charge by irradiating electrons to the sample 9, which takes positive charge. However, there are variations in the charged state of the sample surface, which means that the neutralization of the electrical charge will not always be easy even when utilizing this charge neutralizer 8. Another state of electrical charge is shown in FIGS. 1A and 1B. As int he case of FIG. 1A, where the sample surface is equally charged, irradiation can be performed in a wide range as making an electron shower. But in the case of FIG. 1B, where an isolated pattern made of a material with different resistance on the insulation sample is charged in a limited area, which cannot be neutralized by the irradiation in an electron shower manner. It is therefore effective to focus the electrons to make a beam to irradiate the limited area. Devices are becoming more precise recently, and when observing defective parts of a device using a microscope, neutralization of the electrical charge of the limited area is required. If there is only one form of electrical charge of the sample, it can be dealt with, however, when a phenomenon of electrical charge over a wide area and a phenomenon of electrical charge in a limited area occur at the same time, a charge neutralizer should be adjusted and switched so as to be capable of wide range irradiation or capable of limited area irradiation. However, this switching operation is not only troublesome, but also the response against the switching operation is slow. Namely, it takes a while for the new manner of irradiation to reach a stable state form the switched timing, and the problem arises that it cannot cope with the phenomena.
The purpose of the present invention is to provide a focused ion beam device, having one or a plurality of charge neutralizers, which is capable of achieving a quick and precise neutralization operation for electrical charge over a wide area and electrical charge in a limited area, when both situations exist in the sample in a mixed manner.
The present invention achieves a quick and precise neutralization operaiton for charge up over wide area and charge up in a limited area, when both exist within the sample in a mixed manner, by having a charge neutralizer with a function for neutralizing electrical charge, separately provided for charge up over a wide area and for charge up in a limited area, or by having a charge neutralizer with a scanning function, to scam a beam or to stop at the prescribed area using a deflector, or by having a charge neutralizer with an iris, having a central opening a plurality of openings in the periphery of the central opening, within an optical system.